This invention relates to an improvement in character generators in dot matrix printers. In particular, the invention relates to a method and means for determining when the end of a character shape has been printed and for providing proportionally spaced character printing.
Character generators are used with dot matrix printers of both the non-impact and impact type. Each character of a font is stored in a character generator memory as a character matrix of binary ones and zeros. A selected character matrix controls the printing of a pattern of dots on a page. In laser-xerographic printers, a sweeping laser beam is modulated according to the pattern of ones and zeros found in a portion of the selected character matrix of the character generator. The beam is caused to sweep periodically across a photoconducting drum by a rotating multifaceted mirror. The modulated laser light when it impinges on the photoconducting drum leaves an electrostatic image behind on the drum. Rotation of the drum and multifaceted mirror as well as transmission of the data from the character generator are controlled and synchronized by a printer controller.
One method of printing a line of characters from a character generator with a laser-xerographic printer involves storing each of the character shapes in a standard size character matrix within the character generator memory. Imaging of each character matrix to be printed requires a fixed number of laser sweeps across a fixed number of dot positions in order to print the matrix. A counter or timing circuitry counts the number of dots crossed by the laser as it sweeps across the drum. Each time during the sweep that the count reaches a fixed number it begins over to start another character matrix which is associated with an adjacent character shape to be printed. This method, however, does not allow for proportional spacing between printed characters, that is, although not all character shapes have the same width, all character matrices used to store and print the character shapes are of the same size, and hence each character printed occupies the same amount of space on a page.
Several U.S. patents disclose various approaches for character proportional spacing or the intermixing of various character widths when printing. See U.S. Pat. Nos. 3,165,045; 3,729,714; 3,999,168; 4,044,363; 4,079,458; and 4,107,786. Each of these patents discloses the use of additional counting or timing circuitry sometimes triggered by end of character or pitch bit information contained in the stored character data in order to provide proportional spacing.